To facilitate understanding of the hydrodynamic behaviour of CFBs, a one-dimensional model for the riser tube of a CFB has been developed. The model describes steady state hydrodynamic key variables (i.e. cross-sectional averaged values of pressure, solids concentration and velocities of both phases) for developing axi-symmetrical flow as a function of the axial position in the riser tube. Calculated results have been compared with experimental data obtained from a small scale CFB unit which could be operated at pressures up to 6 bar. Despite the simplicity of the model, it turned out that the model was capable of predicting the effect of changes in operating conditions (i.e. gas velocity, solids mass flux, operating pressure and particle diameter). The model neglects the existence of clustering of particles, lateral solids segregation and solids downflow near the tube wall, which limits the applicability to dilute systems (epsilon(s)<0.04).